Windows take a lot of weather abuse, and their material makes a significant difference in durability and performance.

Wood windows generally require repainting and re-glazing every 2-3 years, which can be drag on a homeowner’s time and patience—or their wallet if they hire a painter.

Although painted aluminum windows can pit, they don’t generally have the same maintenance problems as wood. However, aluminum windows are notorious for poor thermal performance. Much like radiators they conduct unwanted heat from the outside into the room. In the winter, aluminum transfers cold in the same way. This heat transfer creates condensation and related problems. Many modern aluminum windows now utilize “thermal breaks” to address the condensation issue and increase energy efficiency. These “breaks” are made of vinyl.


Vinyl replacement windows are a top choice for home remodeling because vinyl is itself a thermal break, minimizing heat transfer from the outside the home to the inside. Vinyl windows look great, are energy efficient and require very little maintenance. There’s also no need to repaint or restain vinyl windows, since they are the same color throughout.

However, before placing an order for a replacement window, the first critical step is to determine the right measurement for the new window.

How to Measure for Replacements

The simplest method of replacement is to swap the existing window for a new unit of the same size. This is called a pocket replacement and allows the homeowner to keep the trim intact around the windows. Depending on the construction of your windows, it may help to remove the old interior trim to ensure correct measurements of the rough opening. If the window manufacturer offers specific measuring instructions for their particular windows, defer to those guidelines.


When measuring the existing window for width, place the tape against the jamb and measure to the other jamb (not the stop molding or the parting bead, which are wooden strips attached over the jamb). On double-hung windows, the parting bead that separates the sashes will be removed from the jamb when the new windows are installed. Replacement windows are sold in a standard thickness to fit inside the 3-1/4-in. pocket that exists between the outside and inside stops after the parting bead is removed.

Measure the window’s width in three places—top, middle and bottom of the window. Use the smallest of the measurements to determine the width that surrounds the window.

Next, measure the height of the window, placing the tape on the very top of the sill. The sill is not to be confused with the window stool, which is a piece of interior molding at the bottom of the window to give it a finished appearance. On a double-hung window, the sill is the board the sash closes onto. The sill is usually sloped to divert water away from the house, so it is important to strike the measurement from the uppermost point of the sloped sill. Measure from the sill to the top jamb (not a stop or parting bead).

Measure the window’s height in three places—right, center and left of the window. Use the smallest of the measurements to determine the height surrounding the window.

Once you have the measurements of the existing window, consider deducting slightly from your figures so the replacement window will be easier to install. Some professionals suggest deducting 1/4 inch from the width and 1/2 inch from the height. This slightly smaller measurement ensures the installer won’t try to force the new window into place, potentially damaging the unit or affecting its operation. The extra space makes it easier to adjust the new window with shims and allows room to insulate around the unit.

Remember, the replacement window must fit into the opening plumb, level and square, even though the opening may not be any of these.

Most manufacturers will offer standard size windows, and the homeowner/contractor should order a size that most closely matches their measurements, unless they plan to change the size. Keep in mind that if a window is slightly smaller than the window frame, then it can be shimmed to properly fit in the opening. However, if the window is too large, then it won’t fit into the rough opening without substantial reconstruction of the wall.

Some manufacturers such as Simonton Windows customize their windows to the exact measurements requested, and standard sizes do not apply.

Replacing Metal Windows in Brick Homes

Metal windows are generally fastened with a flange inside the wall behind the brick. To measure for replacement, follow the same three-step measuring guidelines but strike the tape from brick to brick to measure the window’s width. To determine height, measure from the brick at the bottom to the lintel at the top of the opening.

Note: The brick opening may be larger than the window opening.

If this is the case always use the smaller of the two openings to determine the size of the replacement.


As shown in the diagram, take three measurements for the window’s height and three measurements for the window’s width. Use the smallest measurement for each dimension.